The Advanced Study Institute on 'Elementary Excitations in Solids, Molecules, and Atoms' was held at the University of Antwerp (U.I.A.) from June 18th till June 30th 1973. The In­ stitute was sponsored by NATO. Co-sponsors were: Agfa-Gevaert N.V. (Mortsel-Belgium), Bell Telephone Mfg. Co. (Antwerp-Belgium), I.B.M. BelgiumN.V. (Brussels-Belgium), the National Science Founda­ tion (Washington D. C. - U. S .A.) and the Uni versi ty of Antwerp (U. I .A.) . A total of 120 lecturers and participants attended the Institute. Over the last few years, substantial progress has been made in the description of the elementary excitations of the elec­ tronic and vibrational systems and their interactions. Parallel with this, the experimentalists have obtained outstanding re­ sults, partly as a result of availability of coherent light sour­ ces from the far infrared through the visible region, and partly because of the availability of synchrotron radiation sources in the soft X-ray region. The results of today will lead to fur­ ther progress over the next years. It was the purpose of this NATO Advanced Study Institute to present a state of the art, namely a survey of experiment and theory.